1. Field of the Invention
This invention relates generally to the field of thin dielectric films. More specifically, the invention relates to the formation of an SrRuO3 film by deposition utilizing independent deposition segments for each of the dissimilar precursor compositions.
2. Description of the Related Art
Barium strontium titanate, BaSrTiO3 is one of the most promising candidates as a dielectric material for post-1-Gbit dynamic random access memory capacitors. However, as device sizes continue to shrink, the thickness of the dielectric must be reduced in order to increase the accumulated charge capacitance and reduce the capacitor area,. In thin dielectric films with thickness on the order of several tens of nm, a low leakage current and a higher dielectric constant are required. However, when a dielectric is made very thin, unwanted changes, such as an increase in leakage current and a decrease in the dielectric constant relative to the bulk, may occur. Although the origins of these phenomena are not completely understood, they are known to depend greatly on the materials used for the capacitor electrodes.
Currently, there are numerous possible candidates for the electrodes used in BaSrTiO3 capacitors, including Pt, Ir, Ru and RuO2. However, SrRuO3 is one of the most promising candidates for an electrode material having an improved performance with respect to capacitance, leakage degradation and lattice match for BaSrTiO3.
In the formation of thin films, layers and coatings on substrates, a wide variety of source materials have been employed. These source materials include reagents and precursor materials of widely varying types, and in various physical states. To achieve highly uniform thickness layers of a conformal character on the substrate, vapor phase deposition has been used widely. In vapor phase deposition, the source material may be of initially solid form which is sublimed or melted and vaporized to provide a desirable vapor phase source reagent. Alternatively, the reagent may be of normally liquid state, which is vaporized, or the reagent may be in the vapor phase in the first instance. Conventionally, these reagents may be used in mixture with one another in a multicomponent fluid which is utilized to deposit a corresponding multicomponent or heterogeneous film material such as SrRuO3. Such advanced thin film materials are increasingly important in the manufacture of microelectronic devices and in the emerging field of nanotechnology. For such applications and their implementation in high volume commercial manufacturing processes, it is essential that the film morphology, composition and stoichiometry be closely controlled. This in turn requires highly reliable and efficient methods for deposition of source reagents to the locus of film formation.
Various technologies well known in the art exist for applying thin films to substrates or other substrates in manufacturing steps for integrated circuits (ICs). For instance, Chemical Vapor Deposition (CVD) is a often-used, commercialized process. Also, a relatively new technology, Atomic Layer Deposition (ALD), a variant of CVD, is now emerging as a potentially superior method for achieving uniformity, excellent step coverage, and transparency to substrate size. ALD however, exhibits a generally lower deposition rate (typically about 100 ang/min) than CVD (typically about 1000 ang/min).
Chemical vapor deposition (CVD) is a particularly attractive method for forming thin film materials such as SrRuO3 because of the conformality, composition control, deposition rates and microstructural homogeneity. Further, it is readily scaled up to production runs and the electronics industry has a wide experience and an established equipment base in the use of CVD technology which can be applied to new CVD processes. In general, the control of key variables such as stoichometry and film thickness and the coating of a wide variety of substrate geometries is possible with CVD. Forming the thin films by CVD permits the integration of SrRuO3 into existing device production technologies.
ALD, although a slower process than CVD, demonstrates a remarkable ability to maintain ultra-uniform thin deposition layers over complex topology. This is at least partially because ALD is not flux dependent as CVD processes are. In other words, CVD requires specific and uniform substrate temperature and precursors to be in a state of uniformity in the process chambers in order to produce a desired layer of uniform thickness on a substrate surface. This flux-independent nature of ALD allows processing at lower temperatures than with conventional CVD processes.
However, in either case, when the film being deposited is a multicomponent material, such as SrRuO3, rather than a pure element, controlling the deposition of the film is critical to obtaining the desired film properties. In the deposition of such materials, which may form films with a wide range of stoichiometries, the controlled delivery of the source reagents into the reactor chamber is essential.
The present invention is directed to controlling the delivery of source reagents into the reactor chamber to produce thin films of SrRuO3.
The present invention is directed to a method of fabricating an SrRuO3 thin film. The method utilizes a multi-step deposition process for the separate control of the Ru reagent, relative to the Sr reagent, which requires a much lower deposition temperature than the Sr reagent.
A Ru reagent gas is supplied by a bubbler and deposited onto a substrate at temperatures below 200xc2x0 C. Following the deposition of the Ru reagent, the Sr liquid reagent is vaporized and deposited onto the Ru layer at temperatures above 200xc2x0 C.